The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
An engine control module (ECM) is typically configured to provide fuel delivery functions for a single liquid fuel, such as gasoline or other liquid fuel blend such as E85. The ECM may determine a cylinder fresh air charge primarily based on a mass air flow (MAF) signal from a MAF sensor. The ECM calculates a required fuel mass using open loop, closed loop and transient fueling algorithms based on the cylinder fresh air charge. During closed loop operation, the ECM monitors oxygen (O2) sensors to correct fueling errors using fuel trim functions. Fuel injector characterization functions are used to convert the required fuel mass into an injector on time, which is executed by fuel injector output drivers of the ECM.
A fuel injector control module (FICM) may be used to enable an engine to operate on alternative gaseous fuels, such as compressed natural gas (CNG) and liquefied petroleum gas (LPG). The FICM is connected between the ECM and fuel injectors of the engine. The FICM has direct control of the fuel injectors for both mono-fuel applications (one fuel storage and delivery system) and bi-fuel applications (two different fuel storage and delivery systems, where each fuel is introduced into combustion chambers of the engine one at a time). The FICM selects which set of fuel injectors (injectors for a first fuel source or injectors for a second fuel source) to activate.
During gasoline operation in a bi-fuel system, the ECM generates and transmits a gasoline injector control waveform which is unchanged by the FICM to the gasoline injectors. During gaseous fuel operation, the FICM modifies the injector control waveform to compensate for gaseous fuel combustion characteristics, gaseous fuel delivery rail pressures and temperatures, manifold absolute pressures (MAPs), differences between gasoline and gaseous fuel dynamics, and differences between gasoline and gaseous fuel injector operating characteristics. The FICM modifies the injector control waveform by intercepting (prevents from being transmitted to the gasoline fuel injectors) fuel injector control signals generated by the ECM. The FICM generates compensated fuel injector signals based on the fuel injector control signals received from the ECM. Gaseous fuel injectors are operated based on the compensated fuel injector signals which are based on the gasoline fuel injector control signals from the ECM.
Closed loop fuel injection operation for emissions control uses an exhaust oxygen sensor to provide feedback to correct open loop fueling errors and impart the necessary relative air fuel ratio (AFR) bias, which is fuel source dependant. The O2 sensor response characteristics are such that fuel control may be lean shifted when operating on gaseous fuels, rather than gasoline. The FICM intercepts or overrides the O2 sensor signal provided to the ECM to compensate for this lean shift. The FICM prevents the O2 sensor signal from being received by the ECM and substitutes a simulated O2 sensor signal generated by the FICM when operating with the gaseous fuel. The FICM passes the O2 sensor signal through to the ECM, unchanged during gasoline operation.
The simulated O2 sensor signal from the FICM is used by the ECM to perform closed loop corrections. These closed loop corrections, based on the simulated O2 sensor signal for operation with a gaseous fuel, cause the ECM to adjust fuel injector command signals accordingly. As a result, the FICM causes the ECM to generate fuel injector command signals with the appropriate relative air fuel ratio (AFR) bias for gaseous fuel source operation. The FICM may include injector drivers that supply sufficient current to operate gaseous fuel injectors for LPG and/or CNG fuel sources. LPG and CNG fuel injectors typically have different electrical characteristics than gasoline injectors (i.e. peak and hold current values are different).